1. Field of the Invention
This invention relates to the packaging art and more particularly to a machine for packaging a substance in closed bags formed from two continuous ribbons of a thin fragile material.
In the medical field, for instance, it is sometimes desirable to include a small bag containing a chemical diffusible therethrough within a blood bag to maintain the pH of the blood in the blood bag. The desired level of diffusibility through the walls of the smaller bag may be obtained by constructing the bag of a very thin polycarbonate membrane, however, such membranes are extremely fragile and must be handled with great care to avoid damage.
2. Description of the Prior Art
Various machines have been proposed for forming and filling packages from a pair of continuous ribbons. Machines of this type are described in U.S. Pat. Nos. 2,166,643, 2,245,827, 3,350,930, 2,420,983, 2,606,412 and 2,759,308. However, the machines disclosed in those patents are unsatisfactory for forming packages from very thin fragile membranes, such as polycarbonate membranes, for a variety of reasons. In the first place, the machines of the listed patents allow substantial contact between the conduit filling the packages and the membrane itself. The prior machines also do not satisfactorily preform the membranes. The membranes are either not preformed into a bag shape at all or are subjected to substantial stress as they are so formed. Very thin polycarbonate membranes are able to withstand only very slight stress and may be damaged if made into a bag and then filled without being preformed to the desired contour or preformed in too stressful a manner.
It is also generally desirable to reduce the amount of air within a package formed from two ribbons to a bare minimum. This is particularly true to the case of polycarbonate bags to be included within blood bags. While some of the machines disclosed in the listed patents may eliminate undesired air deposits within the bags, this is done in the context of mechanisms which are unsatisfactory for use with polycarbonate or other very thin fragile membranes.
Thus, there has been a need for an improved machine able to form and fill packages from two ribbons of a very thin fragile material.